The present application relates to a nonaqueous electrolyte secondary battery using a negative electrode containing a binder.
In recent years, a number of portable electronic appliances such as a camera-integrated VTR (video tape recorder), a digital still camera, a mobile phone, a personal digital assistant and a laptop computer, each achieving a reduction in size and weight, have appeared. With respect to batteries, in particular, secondary batteries as a portable power source for such electronic appliances, intensive studies have been conducted for the purpose of enhancing the energy density.
Of secondary batteries, a lithium ion secondary battery has a structure in which a positive electrode and a negative electrode are laminated or wound via, as a diaphragm, a resin thin film separator made of polypropylene, polyethylene, etc. and includes a nonaqueous electrolyte containing an electrolyte salt and a nonaqueous solvent in the inside thereof.
There are known lithium ion secondary batteries which are provided with a positive electrode using, for example, an aluminum foil as a positive electrode collector, LiCoO2 as a positive electrode active material, graphite as a conductive agent and polyvinylidene fluoride, TEFLON (a registered trademark), etc. as a binder; and a negative electrode using, for example, a copper foil as a negative electrode collector, amorphous carbon, coke, graphite, etc. as a negative electrode active material and polyvinylidene fluoride, polyacrylonitrile, a styrene-butadiene rubber, etc. as a binder (see, for example, JP-A-8-315817, JP-B-7-70319, JP-A-2003-282061, JP-A-2003-317722, Japanese Patent No. 2548460 and JP-A-2003-132893).
Also, there is proposed a polymer lithium ion secondary battery containing a polymer such as polyvinylidene fluoride, polyacrylonitrile and polyethylene oxide as an electrolyte of a lithium ion secondary battery. In particular, in view of the fact that a gel electrolyte battery using a gel electrolyte which has been solidified by incorporating an electrolytic solution into a polymer is free from liquid leakage of the electrolytic solution and high in reliability, the gel electrolyte battery is widely put into practical use. In the gel electrolyte battery, electrolytes existing in the inside of an electrode and between an electrode and a separator are immobilized, and the locations of battery members are fixed.
The polymer lithium ion secondary battery is lightweight because an aluminum laminated film can be used for an exterior thereof; and in the polymer lithium ion secondary battery, it is possible to prepare a thin and large-area battery which is hardly processed when a metal can exterior is used (see, for example, JP-A 2001-167797).